Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

393
FXUS63 KLOT 262357
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
657 PM CDT Sun Apr 26 2026

.KEY MESSAGES...

- Severe thunderstorms Monday with all hazards possible (large
  hail, damaging winds and tornadoes), particularly south of the
  Kankakee/Illinois River Valleys. Heavy rain and localized
  flooding also possible areawide due to multiple rounds of
  thunderstorms.

&&

.DISCUSSION...
Issued at 237 PM CDT Sun Apr 26 2026

Quiet conditions will persist through at least this evening
amid scattered mid/upper-level clouds and steady E/ESE flow at
the surface. Persistent low-level stratus over far northeast
Illinois continues to slowly erode from the south and west. This
stratus deck may expand westward by early evening, but an
expected gradual veering of the winds should advect most/all of
the stratus into southern Wisconsin for most of the night.

Focus remains on the potential for severe convection in the
region Monday into Monday evening, though forecast trends
continue to become more complex/muddled as the event nears.
Regardless of any potential upstream convection tonight into
Monday morning, the kinematic/dynamic/thermodynamic set-up
appears quite favorable for severe storms around the mid-
Mississippi River Valley. A slightly negatively tilted wave and
associated surface low passing over Iowa combined with
impressive upper-level jet forcing/diffluence will provide ample
forcing for initiation by eroding a modest EML. This also means
that coverage of convection will likely become quite high
upstream of our area, suppressing the northward extent of the
unstable warm sector through the day Monday. While guidance has
trended less favorable for severe storms with northward extent,
there are plenty of ingredients still available to support a
notable severe storm threat. Below are a few generalized
scenarios with decreasing likelihood but increasing severe risk:

1) Substantial upstream convection tonight into the morning:

Elevated storms would induce a deep cold pool and focus an
effective warm front toward central Illinois. While steep mid-
level lapse rates would continue to support waves of elevated
convection and perhaps instances of large hail, widespread
severe weather would remain confined south of the forecast area.

2) Some upstream convection tonight into the morning.

Clusters of thunderstorms stemming from both ongoing convection
in eastern Kansas and expected convection over central Kansas
this evening would either weaken or shift toward northern
Illinois, leaving an effective outflow/warm front draped
somewhere across central Illinois by late morning. Additional
convection firing north of this boundary could become rooted at
the surface as the afternoon progresses and offer a focus for
localized organized severe convection, including supercells with
an inherent tornado risk, over the southern CWA in the
afternoon. Strongly forced convection to the west would then
bring a larger QLCS wind and tornado risk for areas south of the
Kankakee/IL River Valleys late afternoon and evening.

3) Little to no upstream convection through Monday morning:

Discrete convection would initiate west of the Mississippi
River and congeal into a QLCS across much of Illinois late
Monday afternoon and evening. Less coverage would support
discrete supercells with all severe hazards extending eastward
across west-central Illinois and possibly into at least the far
southwest CWA. ENE-pointed deep-layer shear vectors would
continue to support embedded supercell elements within the QLCS.
This would favor damaging winds and possible tornadoes with
southward extent where a narrowing higher theta-e axis advects
ahead of the convection.


Regardless of the severe weather potential, flooding remains of
concern given unseasonably high PWATs around 1.5 inches and the
potential for several rounds of convection training over the
same area.

Behind Monday`s system, a transition to longwave troughing over
the eastern Great Lakes and eastern Ontario/Quebec will favor a
cooler end to April and start to May with perhaps a couple
chances for showers later in the week. Nighttime frost potential
will also increase late in the week, specifically for interior
northern Illinois.

Kluber

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 657 PM CDT Sun Apr 26 2026

- A period or two of SHRA/TSRA Monday late morning through
  early/mid evening. Highest thunder chances late afternoon and
  evening.
- Rather strong and gusty southeast winds Monday, shifting to
  southwest late Monday evening.

It`ll be quiet tonight, with VFR conditions and east-southeast
winds. Weather will turn more active Monday as a storm system
moves from the Midwest to the upper Mississippi Valley. Periods
of showers and thunderstorms are expected at the terminals from
late morning through the afternoon, with the threat likely not
ending until Monday evening. Initially, thunderstorm chances
with the first batch of showers looks to be on the lower side,
so just carrying a TEMPO late morning through mid afternoon.
Thunderstorm chances will gradually increase during the
afternoon and especially into the evening. Attempted to frame
the 2 most likely time periods of rain in the TAF (late morning
to mid afternoon and then Monday evening). While there is a
period of no precipitation in the TAFs during the mid-late
afternoon, rain chances aren`t zero, but that looks to be the
most likely time period with mainly dry conditions. Confidence
in the timing of SHRA/TSRA tomorrow is lower than avg and
adjustments to the timing may very well be needed in later TAF
updates.

Winds tomorrow should increase from the southeast and become
increasingly gusty during the morning. General trend would favor
winds gradually becoming closer to due south by late afternoon
into the evening, with sustained winds and gusts potentially
becoming a bit stronger. Shower and thunderstorm activity Monday
could result in some disruptions in the overall wind fields, so
temporary changes in both the magnitude and direction of winds
are possible Monday. If storms don`t disrupt winds too much,
there is a potential for winds close to 180 degrees gusting to
35kt+ for a time late in the afternoon into the early evening,
which could begin to approach crosswind thresholds for ORD.

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 4 AM Monday to 10 AM CDT Tuesday for
     the IL nearshore waters.

     Small Craft Advisory from 10 AM Monday to 10 AM CDT Tuesday
     for the IN nearshore waters.

&&

$$

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